1. Field of the Invention
The present invention relates generally to light emitting instruments and, in particular, to an improved ambient air cooled high intensity light emitting instrument.
2. Description of the Prior Art
Many opportunities for visual inspection require prolonged continuous use of light in order to adequately illuminate the area to be inspected. Hand held medical and dental light sources which provide illumination for inspection or examination are well known and have been utilized for many years. Specific examples of such devices include ophthalmascopes, otoscopes, retinoscopes, and other similar instruments. In these hand held devices, the handle generally houses the light source. It is advantageous to mount the lamp within the instrument rather than in a remote location, requiring the use of additional transmission means such as fiber optics, to direct the light to the desired location. Although a remote light source is easy to cool, it usually results in a relatively inflexible fiber optic cable, significantly limiting the maneuverability of the instrument and increasing the overall cost of the instrument.
Recently, high intensity light sources, such as halogen or krypton gas filled lamps have been developed to provide significantly more light for hand held dental and medical instruments. This increase in light intensity, often two to three times greater than that provided by ordinary vacuum lamps of the same size, greatly improves the performance of these instruments. In addition, vacuum lamps progressively deteriorate in both quantity and quality of light emission as the lamp ages due to tungsten particles which are deposited on the envelope of the lamp. A halogen lamp however, provides a reasonably consistent quantity and quality of light emission over its life, due in part to the extreme lamp skin temperature (250.degree.-300.degree. C.) which causes tungsten particles deposited on the envelope of the lamp to vaporize and redeposit on the tungsten filament.
Unfortunately, this extreme heat generated by high intensity lamps can often lead to other problems for hand held instruments. Obviously, heat buildup within the handle will cause discomfort to the user of the instrument. This problem becomes exaggerated as the duty cycle for the instrument increases. Some dental or surgical procedures require a hand held instrument to be used continuously for extended periods of time, such as an hour or more. Other heat related problems inherent in these instruments include accelerated deterioration of the lamp and instrument materials, and potential injury to the person on whom the instrument is used.
The problem of heat build up in hand held instruments using high intensity lamps has been addressed several times in the prior art. U.S. Pat. Nos. 4,334,863; 4,477,252; and 5,033,960 all teach specific solutions to the problem of heat generation within the handle of dental instruments. U.S. Pat. Nos. 4,334,863 and 4,477,252 each teach a dental handpiece in which air used to drive the handpiece is also used to cool the heat generated by the fiber optic system mounted within the handpiece, while U.S. Pat. No. 5,033,960 teaches a device which channels exhaust air from the dental handpiece to flow laterally into the lamp socket to cool the lamp used in its fiber optic system.
Another problem associated with the use of hand held medical and dental instruments is contamination. It is well known in the practice of medicine and dentistry that great care must be taken to protect against diseases transmitted by cross contamination. Many serious diseases, including hepatitis and the deadly disease AIDS, can be transmitted by cross contamination. The most effective method of controlling cross contamination when using medical instruments is sterilization. The usual method of sterilization of instruments of this type is autoclaving. The autoclaving procedure requires subjecting the instrument to an environment of pressurized steam at 250.degree. F. for an extended period of time. One potential problem in light emitting instruments after autoclaving is residual moisture, which could cause a short in the electrical circuitry of the instrument during operation. Therefore, is important that the circuitry of the instrument is adequately sealed to prevent both contamination and autoclaving steam from contacting the circuitry.
However, while sealing the circuitry areas of the instrument protects it from residual moisture, it also acts to keep heat trapped within this area. Thus, the ability of the instrument to dissipate heat adequately is much more imperative.